Electric discharge tube



Fceb, 27, @3 10 A. BOUWERS ELECTRIC DISCHARGE TUBE Filed Jan. 27, 1-925 Mag 3W 2 Sheets-Sheet l Feb. 27 39340 A'. BOUWERS L fi ELECTRIC DISCHARGE TUBE Filed Jan. 27, 1925 2 Sheets-Sheet 2 Patented Feb. 27, 1934 UNITED STATES nmc'rmc DISCHARGE TUBE Albert Bouwers, Eindhoven,

Netherlands, a!-

signor to N. V. Philips Gloeilampenfabrieken, Emdhoven, Netherlands Application January 27, 1925, Serial No. 5,108 In the Netherlands, June 4, 1924 11 Claims.

' tubes for Rontgen-therapeutics, operating with potentials of 200,000 volts and higher, have the disadvantage that it is very dificult to construct the insulation between the anode (anti-cathode) and the cathode in such a manner as to be capable of resisting this very high potential diiierence in -the long run.

According to the invention, in order to obviate this disadvantage, members of a discharge tube, between which during the operation a very high potential difference occurs, are connected to each other by a wall which consists of parts of insulating material alternated by one or more parts of conductive material.

The parts of conductive material are preferably adapted to allow a desired potential to be impressed on them. In this manner it is possible to divide the total potential difference between the ends of the connecting wall equally over the insulating parts, owing to which the total insulating length-of these parts together may be materially smaller than the insulating length of one insulating piece would have to be. If from the exterior the conductive parts are not brought to determine potentials, the division of the potential over the insulating parts will not generally be equal, although in some applications it may be possible to choose the construction such that the conductive parts automatically take such potentials that this equal distribution is obtained.

According to another feature of the invention the connecting wall may consist of glass parts alternated by metal parts which are sealed thereto.

According to a urther feature of the invention that part of t e outer wall of the tube which connects the cathode and the anode to each other, may consist of insulating and conductive parts.

In the latter embodiment of the invention the outer wall of the tube may further consist for a considerable portion of a metal part or section having on both sides sealed to it, glass parts, one of which is hermetically connected to the cathode or to a member having during the operation a similar potential, the other being connected to the anode or to a member having during the operation a similar potential.

If the invention is applied to X-ray tubes with an incandescent cathode, the metal part is preferably so arranged as to surround the head of the anti-cathode and the incandescent cathode together with the device for directing the cathoderays on a limited portion of the anti-cathode. This device may consist of a focussing device as is made use of in Coolidge tubes or again of a metal vessel which surrounds the incandescent cathode and which is so constricted on the side of the anti-cathode that the cathode-rays are forced to strike the anti-cathode on a limited surface. This metal vessel has preferably a potential which is slightly negative relatively to all points of the incandescent cathode.

When operating a discharge tube according to the invention, the conductive parts of the connecting wall assume such potentials that the total potential difference occurring between the ends of the connecting wall is equally divided over the insulating parts of the said wall. When operating a discharge tube according to the invention in which a metal part of the outer wall is arranged between two insulating parts, this metal part is preferably grounded.

Other characteristics of the invention will become clear from the accompanying drawings and their description.

The accompanying drawings illustrate, by way of example, X-ray tubes to which the invention is applied. It may however be observed once more that the invention is not restricted to X-ray tubes, but may be applied in general to'discharge tubes with two or more electrodes particularly those operating with very high tensions of, for example, 200,000 volts or higher.

Figure 1 represents an X-ray tube according to the invention with its connections, having the incandescent cathode arranged within a metal vessel of special construction, through which vessel likewise the active X-rays pass.

Figure 2 illustrates an X-ray tube in which the incandescent cathode is arranged within a focussing device as is made use of in Coolidge tubes.

Figure 3 showsa different construction, in which just as in the tube shewn in Figure 1, the incandescent cathode is arranged within a metal vessel of special construction, but in which the X-rays pass out sidewards of the cylindrical tube.

In the X-ray tube shewn in Figure 1, the cylindrical outer wall consists of a glass part 1 to which a re-entrant glass tube 2 is hermetically sealed, a metal part or section 6 and a second glass part 7 to which a re-entrant conical glass part 8 is hermetically sealed. An anti-cathode 3 is hermetically sealed at its edge to the end of the tube 2. An insert 4 made for example of tungsten, is secured to the front face of the anticathode which, for example, may consist of chrome-iron; a metal tube 5 serves to supply a cooling liquid to the anti-cathode.

At both its edges the metal vessel or sleeve 6 is hermetically sealed to the glass parts 1 and 7. The'part 6 may, preferably, consist of chromeiron of suitable composition, which material may be sealed very well to glass, is practically nonporous and is easily deprived of occluded gases. 1

0n the inner side the glass tube 8 is hermetically closed by a window 9 for the passage of the X-rays and has sealed to its inner end a metal vessel 10. An incandescent cathode 1l, consisting, for example, of tungsten, is carried within the vessel 10 by leading-in wires 12 and 13 which are insulated from the vessel 10 by means of beads 14 and 15 of quartz or similar material. The leading-in wires 12 and 13 as well as a leading-in wire 16 for the vessel 10 are sealed into the glass wall 7.

On the side towards the anti-cathode the metal vessel 10 is narrowed to an aperture 17 for the passage of the cathode-rays. On operating the tube, a high potential is supplied between the incandescent cathode 11 and the anti-cathode 3; the vessel 10 is given a potential being preferably about equal to that of the filament. Owing to the peculiar shape of the metal vessel 10 and to the arrangement of this vessel and the anticathode relative to each other, the electrons emitted by the filament are forced to strike the front face of the anti-cathode on a limited surface. It will be observed that the active X-rays leave the surface of the anti-cathode at right angles or substantially right angles thereto and then take their way through the metal vessel 10. If this vessel consists of chrome-iron or similar material, X-rays striking on the wall of this vessel will be absorbed so that they cannot exert a detrimental influence on places where they are not wanted.

To the anti-cathode 3 is secured a bell-shaped metal member 18 which serves to prevent cathode-rays from striking the welds between the metal and the glass in the tube, especially between the metal part 6 and the glass parts 1 and 7. In operating the tube, the metal part 6 is preferably grounded whilst the total high potential which has to be supplied between the incandescent cathode and the anti-cathode, is equally divided between the anti-cathode 3 and the metal part 6 and between the metal vessel 10 or the incandescent cathode and the metal part 6. The insulation between the metalpart 6 and the anticathode or the incandescent cathode need therefore only resist half of the potential of the tube. The construction oifers the incidental advantage that use may be made of high potential transformers with a secondary winding which is grounded in the middle, as appears from the connection also shown in Figure 1.

In the installation illustrated in Figure 1, the anti-cathode is connected to one end of a secondary winding 23 of a high potential transformer, the primary winding 20 of which may be connected to some suitable source of voltage with the interposition of a regulable resistance 21 and a bipolar switch 22. The other end of the high potential winding 23 is in connection with an incandescent cathode 11, the middle of the winding being electrically connected to the grounded metal vessel 6.

The incandescent cathode 11 receives current from a secondary winding 25 of a transformer, the primary winding 24 of which may be connected to a source of voltage via a regulable resistance 26 and the switch 22.

metal vessel 10 are separately led through the outer wall of the discharge tube in order to allow a suitable potential to be supplied between the incandescent cathode and the vessel. It may, for example, be desirable to take care that the vessel obtains a negative potential relative to the filament.

In the construction shown in Figure 2 an anticathode 30 and an incandescent cathode 31 are arranged inside a cylindrical wall consisting of glass parts 32 and 34 and a metal part or waist section 33. At its edge the anti-cathode is hermetically sealed to a glass tube 34, whilst the incandescent cathode is arranged within a metal vessel 35 which serves as a focussing device in the same manner as is usual in Coolidge tubes. The vessel 35 is carried by metal supports 36, and wires 37 and 38 serve to supply current to the incandescent cathode.

A window 39 for the passage of the X-rays is provided in the wall of the metal part 33. The axis of the beam of the X-rays is directed at right angles to the main axis of the tube. The part 33 may be grounded, so that the portion of the tube which is turned towards the patient, is not dangerous; at the same time it may serve to screen undesirable or stray X-rays. It may be made, for example, of chrome-iron.

In the construction shown in Figure 3, an anticathode 40 is hermetically sealed to a glass tube 41; a tube 42 serves to supply the cooling liquid to the anti-cathode. The cylindrical outer wall of the tube consists of glass parts 43 and 45, having sealed to them a metal sleeve 44 which surrounds the anti-cathode 40 and an incandescent cathode 49 with a corresponding metal vessel 47 for a considerable portion. The metal vessel 47 is hermetically sealed to a glass tube 46 and is constricted on the side of the anti-cathode to an opening 48 for the passage of the cathode and X-rays. The incandescent cathode 49 which is insulated from the metal vessel 47 is provided with leading-in wires 51 and 52, the metal vessel 47 with a leading-in wire 50.

The active X-rays pass through the metal vessel 4'7 and then pass through a window 53.

The metal vessel 47 preferably obtains about 130 the same potential as the incandescent cathode, the metal sleeve 44 is preferably grounded, whilst the potential differences between the metal sleeve 44 and the anti-cathode 40 on one side and this metal sleeve and the incandescent cathode on the other side are taken about equal.

X-ray tubes as illustrated may be used, for example, for therapeutic purposes. Even if the potentials are very high, the tubes may be so constructed as to have comparatively small dimensions. Besides, the tal part of sleeve forming part of the outer w 1 may be grounded so that this part of the tube is not dangerous and this metal sleeve may further serve to absorb undesirable X-rays, so that consequently the application of the invention to X-ray tubes offers several advantages.

The X-ray tube as illustrated, may be highly evacuated in some known manner, so that the discharge occurs practically without gas ionization. The tube may also be provided with a gaseous filling consisting of hydrogen or helium having such a pressure that there does not occur any detrimental gas ionization. This pressure may be above 0.0006 millimeters of mercury and, for example, in the case of helium-filling it may amount to about 0.01 millimeters of mercury.

What I claim is:

1. An electric discharge tube comprising a cathode and an anode spaced apart to provide a r50 Iii) that are circumferentially sealed to both sides of the metal section and are connected to the said cathode and anode respectively, each of the said glass parts being of substantially equal insulating capacity and length and each constructed to withstand potentials as high as one-half the operating voltage of the tube.

2. An X-ray tube comprising an incandesoible cathode, an anti-cathode and a device associated therewith for directing the cathode rays on a limited surface of the anti-cathode, and an outer wall or envelope of the tube consisting of glass parts alternated by at least one metal part which extends longitudinally of the tube and surrounds a considerable portion of the head of the anti cathode, the incandescible cathode and the said device, said glass parts being of substantially equal insulating capacity and constructed to insulate said metal part for high potentials of the same order of magnitude from the cathode and said device at one end of the tube and the anode at the other end thereof.

3. An X-ray tube comprising an incandescible cathode, an anti-cathode and a device for focusing the cathode rays on a limited surface of the anticathode, said anti-cathode being arranged to direct the beam of X-rays substantially at right angles to the axis of the tube, a cylindrical envelope consisting of glass parts substantially similar in extent and alternated by at least one metal part at the mid-section thereof, the said mid-section constituting a metal sleeve insulated by said glass parts for high potentials of the same order of magnitude from the cathode at one end of the tube and the anti-cathode at the other end thereof and surrounding for a considerable portion the heads of said cathode and anticathode and the said device.

a. An electric discharge tube having. cathode and anode members between which during the operation of the tube a high potential difierence occurs, and a wall which mechanically connects said members, the said wall consisting of end parts of insulating material substantially similar in extent and alternated by at least one part of conductive material, said part of conductive material during operation of the tube assuming a potential that is substantially midway between the potentials of the two mechanically connected members of the tube.

5. An X-ray tube comprising an envelope, and cooperating cathode and target elements supported therein, the said envelope consisting in part of a metallic sleeve member which encloses the operative parts of said elements and which during the operation of the tube assumes a potential that is substantially equi-distant from the potential of each of said elements, said sleeve member being insulated from said elements by the end portions of said envelope, the said end portions of the envelope being of substantially equal insulating capacity and length.

6. An electric discharge tube comprising cooperating spaced cathode and anode electrodes between which during the operation of the tube a high potential difierence occurs, and an envelope which supports and electrically insulates the said electrodes from each other, the wall of the envelope consisting of an insulating portion adjacent each electrode and of a metallic waist portion which encloses the operative parts of the electrodes and extends toward the ends of the,

tube in both directions to points beyond the space between the electrodes, the said insulating portions being each of substantially the same insulating capacity and length and each constructed to withstand high potentials.

7. An electric discharge tube comprising cathode and anode members between which, during the operation of the tube, a high potential difference occurs, the said members being spaced apart longitudinally of the tube to provide a discharge gap, and a wall or envelope mechanically connecting the said members and comprising at least one part of conductive material which extends longitudinally of the tube in both directions beyond the said discharge gap, and insulating bodies of substantially equal insulating capacity and length each constructed to withstand potentials at least as high as one-half the operating voltage of the tube serving to insulate the said conductive part of the wall from each of said members.

8. An electric discharge tube comprising cathode and anode members between which, during the operation of the tube, a high potential difference occurs, said members being spaced apart longitudinally of the tube to provide a discharge gap, and a wall mechanically connecting said members comprising glass parts and at least one intermediate metal part that extends longitudinally of the tube in both directions beyond the said discharge gap, at least two of the glass parts of the wall being of substantially equal insulating capacity and each formed with a re-entrant portion and each being capable of withstanding a substantial part of the operating voltage of the tube.

9. An electric discharge tube comprising cathode and anode members between which, during the operation of the tube, a high potential difference occurs, the said members being spaced apart longitudinally of the tube to provide a discharge gap, and. a wall or envelope connecting said electrode members, the said wall consisting of glass parts of substantially the same length alternated by at least one metal part sealed to said glass parts, the metal part of the wall being mounted between the two glass parts and extending longitudinally of the tube in both directions beyond the gap between the said members.

10. An X-ray tube comprising an envelope, and cooperating cathode and target elements supported therein, the said envelope consisting in part of insulating portions of substantially equal insulating capacity and length, and a metallic sleeve member which encloses the operative parts of said elements and is mechanically connected to said elements by the said insulating portions of the envelope, said sleeve member being provided with a window for transmitting X-rays.

11. An X-ray tube comprising an envelope, anode and cathode elements supported therein, said elements being spaced apart longitudinally of the tube to provide a discharge gap, said envelope including a metallic sleeve member which surrounds the discharge gap and extends longitudinally of the tube in both directions beyond said discharge gap, said member being symmetrically positioned with respect to said elements and insulated therefrom so that it assumes during the operation of the tube a potential that is substantially equi-distant from the potential of each of said elements. ALBERT BOUWERS. 

